1. Field of the Invention
The present invention relates to a plasma processing equipment which is used to process an object with electron-beam excited plasma. More particularly, the present invention relates to a structure of a process chamber for ionizing a process gas and processing an object and a structure of its peripheral portion.
2. Description of the Related Art
The electron-beam excited plasma processing equipment is widely used for the plasma processing, i.e., plasma ion plating, plasma CVD, plasma sputtering, plasma etching, etc. The electron-beam excited plasma processing equipment comprises a discharge chamber which is filled with the discharge plasma being generated by ionizing the inert gas, and a process chamber in which various reactions are generated by ionizing the process gas by virtue of the electron beam which is extracted from the discharge plasma via the orifice and then accelerated by the accelerating electrode.
As well known in the art, the cathode, the intermediate electrode, the discharge electrode, and the accelerating electrode are arranged in the discharge chamber. When the discharge voltage is applied between the cathode and the discharge electrode, thermions which are discharged from the cathode act to the inert gas which is supplied to the cathode portion to generate the discharge plasma, and thus such discharge plasma fills a space between the intermediate electrode and the discharge electrode in the discharge chamber. Thus, when the accelerating voltage is applied between the discharge electrode and the accelerating electrode, electrons are extracted from the discharge plasma in the discharge chamber and then accelerated to supply the large-current electron beam to the process chamber.
Various process gases such as a silane gas, a methane gas, etc. are supplied to the process chamber in response to the necessity of the reaction process. Various plasma processes are carried out on a surface of the object loaded in the process chamber, e.g., activated species (radicals) are generated by ionizing and dissociating the reactive process gas by means of the electron beam and then deposited on a substrate. Ions in the plasma are injected vertically into the object in accordance with difference between the plasma potential and the object surface potential, or the like.
In the electron-beam excited plasma processing equipment in which the accelerated electron beam is injected in the vertical direction to the object surface, if a gas pressure in the process chamber is low, a high energy component of the beam is irradiated directly into the object and thus a physical etching action of the ions with high energy is increased on the object surface. Therefore, the surface of the object is damaged or the film forming process cannot be performed succeedingly. In addition, for example, in the case of DRAM etching, defects such as degradation or destruction of a gate oxide film is caused since a floating potential on the object surface is distributed over the overall object.
It is effective against above problems to increase the number of times of collision of the beam with gas particles by increasing a gas pressure, or to attenuate the high energy component of the beam by increasing a distance between an irradiation port of the electron beam and the object. However, if the gas pressure is increased, the plasma density near the port of the electron beam becomes higher because the number of collision times increases, and the plasma can not be spread widely.
As a result, uniform plasma with a large diameter can not be obtained.
Therefore, such a problem is caused that uniformity of the plasm reaction on the object surface is deteriorated. Also, to increase the distance is not preferable because a size of the equipment is enlarged.
Meanwhile, there is a beam parallel injection type electron-beam excited plasma processing equipment in which the electron beam is accelerated in the direction parallel with the object surface not to directly irradiate the high energy component of the beam onto the object.
According to this equipment, since the object surface is set in parallel with an electron beam axis in the process chamber and thus the high energy component of the beam is not directly irradiated onto the object, the floating potential on the object surface has a gentle distribution.
However, the plasma density is high near the accelerating electrode but such plasma density is reduced as a location becomes remote from the accelerating electrode. Therefore, there is such a problem that the film forming rate, etc. are different on the upstream side and the downstream side of the electron beam on the object surface and thus the film quality, etc. are not uniform. Moreover, especially it is difficult to fabricate the object with a large area.
In both plasma processing equipments, since the electrons are supplied via a single extracting orifice, the plasma density to be generated is limited.
As described above, in the technical field of the electron-beam excited plasma processing equipment, such problems are treated in the related art that the object having the larger area should be formed by relaxing the ion impact action and that the object should be fabricated effectively by increasing the material plasma density and improving the uniformity of the plasma.
In order to overcome such problem, the ring type electron-beam excited plasma processing equipment has been proposed.
In this equipment, a plurality of extracting orifices for extracting the electrons from the discharge chamber which is filled with the discharge plasma are provided radially such that their electron extracting directions are set in the substantially vertical direction to the electron incident direction toward the discharge portion. Then, the process gas in the process chamber can be ionized by extracting and accelerating the electron beam by virtue of the accelerating electrode being provided in the process chamber, and then the plasma can be applied to the object surface which is provided in substantially parallel with the electron extracting direction.
In this equipment, since a number of extracting orifices are arranged radially in the compartment being projected into the process chamber, the plasma density in the process chamber can be enhanced by extracting the large-current electron flow from the discharge chamber to thus improve an efficiency of the plasma reaction. In addition, since the high energy component of the beam does nut directly collide with the object surface and thus the uneven physical etching action, etc. can be eliminated, uniform process can be applied to the large area object.
Furthermore, since the accelerating electrode is provided separately from the inner wall of the process chamber, an amount of the plasma which flows into the inner wall of the process chamber can be reduced to thus suppress the increase of the inner wall temperature. Therefore, generation of the impurity from the inner wall and entering of the impurity into the formed film can be prevented.
If the self-heating type accelerating electrode is employed in the equipment, the insulating DLC (diamond-like-carbon) which is deposited onto the accelerating electrode as a film when a methane gas is used as the process gas can be changed in quality into the conductive graphite. Therefore, the stable discharge can be maintained for a long period of time.
However, in the ring type electron-beam excited plasma processing equipment, the distance between the object table and the electron extracting ports of the discharge electrode must be set sufficiently large to assure the uniformity of the plasma, and also the film forming rate cannot be enoughly increased because the plasma density is lowered when the object with the large area is treated. In addition, if the distance between the electron extracting ports and the accelerating electrode is increased to treat the object with the large area, the acceleration be unstable when a high-pressure process gas is employed so as to increase the film forming rate.
In this way, the limitation is imposed on the object area as the object and also the limitation is imposed on the increase in the film forming rate.
Also, since the applied power is limited in the equipment which has only one discharge portion for generating the discharge plasma, the film forming rate cannot be increased and the partition is damaged because the power is concentrated to the orifice. Further, since the equipment in the related art has the small power, a decomposition efficiency of the process gas is low and also the process gas is used wastefully, so that a production cost is raised.
Furthermore, since the plasma distribution is limited in the equipment in the related art, the relatively uniform surface action can be applied only to the circular object. As a result, it is difficult for the equipment in the related art to process the large-size square glass substrate, etc.